G. Masetti

The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.

The 40 MHz bunched muon beam set up at CERN was used in May 2003 to make a full test of the drift tubes local muon trigger. The main goal of the test was to prove that the integration of the various devices located on a muon chamber was adequately done both on the hardware and software side of the system. Furthermore the test provided complete information about the general performance of the trigger algorithms in terms of efficiency and noise. Data were collected with the default configuration of the trigger devices and with several alternative configurations at various angles of incidence of the beam. Tests on noise suppression and di-muon trigger capability were performed.

Silicon Drift Detectors (SDDs) have been selected to equip the two intermediate layers of the Inner Tracking System (ITS), of the ALICE experiment, since they couple a very good multitrack capability with dE/dx information and excellent spatial resolution as described in references. In this paper we describe the different components of the SDD system as well as the procedures of the system assembly.

The powerful muon and tracker systems of the CMS detector together with dedicated reconstruction software allow precise and efficient measurement of muon tracks originating from proton-proton collisions. The standard muon reconstruction algorithms, however, are inadequate to deal with muons that do not originate from collisions. This note discusses the design, implementation, and performance results of a dedicated cosmic muon track reconstruction algorithm, which features pattern recognition optimized for muons that are not coming from the interaction point, i.e., cosmic muons and beam-halo muons. To evaluate the performance of the new algorithm, data taken during Cosmic Challenge phases I and II were studied and compared with simulated cosmic data. In addition, a variety of more general topologies of cosmic muons and beam-halo muons were studied using simulated data to demonstrate some key features of the new algorithm.

The increase of luminosity expected by LHC during Phase1 will impose tighter constraints for rate reduction in order to maintain high efficiency in the CMS Level1 trigger system. The TwinMux system is the early layer of the muon barrel region that concentrates the information from different subdetectors: Drift Tubes, Resistive Plate Chambers and Outer Hadron Calorimeter. It arranges the slow optical trigger links from the detector chambers into faster links (10 Gbps) that are sent in multiple copies to the track finders. Results from collision runs, that confirm the satisfactory operation of the trigger system up to the output of the barrel track finder, will be shown.

Correlations among hadrons with the same electric charge produced in Z0 decays are studied using the high statistics data collected from 1991 through 1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth order are used to measure genuine particle correlations as a function of the size of phase space domains in rapidity, azimuthal angle and transverse momentum. Both all-charge and like-sign particle combinations show strong positive genuine correlations. One-dimensional cumulants initially increase rapidly with decreasing size of the phase space cells but saturate quickly. In contrast, cumulants in two- and three-dimensional domains continue to increase. The strong rise of the cumulants for all-charge multiplets is increasingly driven by that of like-sign multiplets. This points to the likely influence of Bose–Einstein correlations. Some of the recently proposed algorithms to simulate Bose–Einstein effects, implemented in the Monte Carlo model Pythia, are found to reproduce reasonably well the measured second- and higher-order correlations between particles with the same charge as well as those in all-charge particle multiplets.

Two drift tubes (DTs) chambers of the CMS muon barrel system were exposed to a 40 MHz bunched muon beam at the CERN SPS, and for the first time the whole CMS Level-1 DTs-based trigger system chain was tested. Data at different energies and inclination angles of the incident muon beam were collected, as well as data with and without an iron absorber placed between the two chambers, to simulate the electromagnetic shower development in CMS. Special data-taking runs were dedicated to test for the first time the Track Finder system, which reconstructs track trigger candidates by performing a proper matching of the muon segments delivered by the two chambers. The present paper describes the results of these measurements.

The ALICE experiment at the LHC will study collisions of heavy-ions at a centre-of-mass energy ∼5.5TeV per nucleon. The main aim of the experiment is to study in detail the behaviour of nuclear matter at high densities and temperatures, in view of probing deconfinement and chiral symmetry restoration. Silicon Drift Detectors (SDDs) have been selected to equip the two intermediate layers of the ALICE Inner Tracking System (ITS) [ALICE Collaboration, Technical Design Report, CERN/LHCC 99–12], since they couple a very good multi-track capability with dE/dx information and excellent spatial resolution as described in [E. Gatti, P. Rehak, Nucl. Instr. and Meth. A 225 (1984) 608; S. Beolé, et al., Nucl. Instr. and Meth. A 377 (1996) 393; S. Beolé, et al., Il Nuovo Cimento 109A (9) (1996)]. In this paper we describe the different components of the SDD system as well as the different procedure of the system assembly.

The drift tubes based CMS barrel muon trigger, which uses self-triggering arrays of drift tubes, is able to perform the identification of the muon parent bunch crossing using a rather sophisticated algorithm. The identification is unique only if the trigger chain is correctly synchronized. Some beam test time was devoted to take data useful to investigate the synchronization of the trigger electronics with the machine clock. Possible alternatives were verified and the dependence on muon track properties was studied.

These proceedings collect the presentations given at the first three meetings of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC", held at the Frascati National Laboratories in 2006. The first part of these proceedings contains pedagogical introductions to several basic topics of both theoretical and experimental high pT LHC physics. The second part collects more specialised presentations.

The barrel region of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider is instrumented with Drift Tube (DT) detectors. This paper describes in full details the calibration of the DT hit reconstruction algorithm. After inter-channel synchronization has been verified through the appropriate hardware procedure, the time pedestals are extracted directly from the distribution of the recorded times. Further corrections for time-of-flight and time of signal propagation are applied as soon as the three-dimensional hit position within the DT chamber is known. The different effects of the time pedestal miscalibration on the two main hit reconstruction algorithms are shown. The drift velocity calibration algorithm is based on the meantimer technique. Different meantimer relations for different track angles and patterns of hit cells are used. This algorithm can also be used to determine the uncertainty on the reconstructed hit position.

The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (∼ O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.

The CMS muon barrel drift tubes system has been recently fully installed and commissioned in the experiment. The performance and the current status of the detector are briefly presented and discussed.

The event display and data quality monitoring visualisation systems are especially crucial for commissioning CMS in the imminent CMS physics run at the LHC. They have already proved invaluable for the CMS magnet test and cosmic challenge. We describe how these systems are used to navigate and filter the immense amounts of complex event data from the CMS detector and prepare clear and flexible views of the salient features to the shift crews and offline users. These allow shift staff and experts to navigate from a top-level general view to very specific monitoring elements in real time to help validate data quality and ascertain causes of problems. We describe how events may be accessed in the higher level trigger filter farm, at the CERN Tier-0 centre, and in offsite centres to help ensure good data quality at all points in the data processing workflow. Emphasis has been placed on deployment issues in order to ensure that experts and general users may use the visualization systems at CERN, in remote operations and monitoring centres offsite, and from their own desktops.

During the High Luminosity LHC, the Drift Tube chambers installed in the CMS detector need to operate with an integrated dose ten times higher than expected at the LHC due to the increase in integrated luminosity from 300 fb-1 to 3000 fb-1. Irradiations have been performed to assess the performance of the detector under such conditions and to characterize the radiation aging of the detector. The presented analysis focuses on the behaviour of the high voltage currents and the dose measurements needed to extrapolate the results to High Luminosity conditions, using data from the photon irradiation campaign at GIF++ in 2016 as well as the efficiency analysis from the irradiation campaign started in 2017. Although the single-wire loss of high voltage gain observed of 70% is very high, the muon reconstruction efficiency is expected to decrease less than 20% during the full duration of High Luminosity LHC in the areas under highest irradiation.

A key component of the CMS (Compact Muon Solenoid) experiment is its muon system. The tracking and triggering of muons in the central part relies on Drift Tube (DT) chambers. In 2013 and 2014 a number of improvements and upgrades were implemented, in particular concerning the readout and trigger electronics. The increase of luminosity expected by LHC will impose several constraints for rate reduction while maintaining high efficiency in the CMS Level 1 trigger system. In order to exploit the muon detector redundancy, a new trigger system has been designed. The TwinMux system is the early layer of the muon barrel region that combines the primitives information from different subdetectors: DT, Resistive Plate Chambers (RPC) and Outer Hadron Calorimeter (HO). Regarding the long term operation of the DT system, in order to cope with up to a factor 2 nominal LHC luminosity, several improvements will be implemented. The in-chamber local electronics will be modified to cope with the new rate and radiation environment. This paper will present, along with the main system improvements implemented in the system, the first performance results from data collected at 13 TeV center-of-mass energy during 2016, confirming the satisfactory operation of both DT performance and the TwinMux system. A review of the present status and plans for the DT system upgrades will be also described.

Recent results on searches for Beyond Standard Model production of Higgs bosons in fermion decay channels are presented. The analyses are based on proton-proton collision data recorded by the CMS experiment at 7, 8, and 13 TeV centre-of-mass energies. The exclusion limits determined by the null results of the searches are interpreted in the framework of models that include extensions of the standard Higgs sector.

Recent results on searches for Beyond Standard Model production of Higgs bosons in fermion decay channels are presented. The analyses are based on proton-proton collision data recorded by the CMS experiment at 7, 8, and 13 TeV centre-of-mass energies. The exclusion limits determined by the null results of the searches are interpreted in the framework of models that include extensions of the standard Higgs sector.

The flat-band voltage VFB of metal-oxide semiconductor structures stabilized with phosphosilicate-glass (PSG) films is studied as a function of the film deposition conditions. It is found that the PSG layers can induce an alteration in the value of the ’’initial’’ VFB which, however, can be completely eliminated by depositing these layers in a pure nitrogen ambient and annealing them for 10 min at 1100 °C in N2. The results are explained in terms of an oxidation-induced fixed oxide charge model.

After several months of installation and commissioning of the CMS (Compact Muon Solenoid) DT (Drift Tube) electronics, the system has finally been operated under magnetic field during the so-called CRAFT (Cosmic Run at Four Tesla) exercise. Over 4 weeks, the full detector has been running continuously under magnetic field and managed to acquire more than 300 million cosmic muons. The performance of the trigger and data acquisition systems during this period has been very satisfactory. The main results concerning stability and reliability of the detector are presented and discussed. I. THE CMS BARREL DRIFT TUBE SYSTEM. The Compact Muon Solenoid (CMS) [1] is a general purpose detector designed to run at the highest luminosity at the LHC collider. The central feature of the CMS apparatus is a superconducting solenoid of 6 m diameter that generates a magnetic field of up to 4 Tesla. Such a high field was chosen in order to allow the construction of a compact tracking system on its interior, and still performing good muon tracking on the exterior. Muons are measured in CMS by means of three different technologies of gaseous detectors. In the barrel, where the magnitude of the residual magnetic field is of the order of 2 Tesla in the iron return yoke and the neutron background and muon rate are expected to be as low as a few Hz/cm, DTs (Drift Tubes) are used [2]. The drift tube chambers are responsible for muon detection and precise momentum measurement over a wide range of energies. The DT system also provides a reliable and robust trigger system with precise bunch crossing assignment, complemented by a set of Resistive Plate Chambers (RPC) which provides redundancy in the trigger. The DT chambers are installed in the five wheels of the return yoke of the CMS magnet (named YB-2, YB-1, YB0, YB+1 and YB+2). Each wheel is divided in 12 sectors each covering ~30o around the interaction point and each sector is organized in four stations of DT chambers named MB1, MB2, MB3 and MB4 going from inside to outside, where MB stands for Muon Barrel. There are a total of 250 DT chambers in CMS. A schematic view of one CMS wheel is shown in figure 1. A DT chamber is made of three (or two in MB4) Superlayers (SL), each made by four layers of rectangular drift cells staggered by half a tube width. The wires in the two inner and outer SLs are parallel to the beam line and provide the track measurement in the magnetic bending plane (r, φ). In the central SL, the wires are orthogonal to the beam line and measure the θ position along the beam. The central θmeasuring SL is not present in the MB4 chambers, which therefore measure only the φ coordinate. The basic element of the DT chamber is the drift tube, which has cross section dimensions of 13 by 42 mm. The total number of sensitive cells is around 172,000. Any charged particle going through a cell volume will generate a signal (hit) in its anodic wire that will be amplified and discriminated by the front-end electronics before being sent to the read-out boards in order to perform time digitalization. The position of the charged particle can be related to the time measurement since the drift velocity in the cell volume is constant. Each cell provides a resolution of 250 μm, and the 100 μm target chamber resolution is achieved by the 8 track points measured in the two (r-φ) SL. Figure 1: Transverse view of a CMS Barrel Yoke Wheel. A. DT Read-out Electronics DT read-out electronics is designed to perform time measurement of the chamber signals that will allow the reconstruction of charged particle tracks. There are several levels of data merging in order to achieve a read-out of the full detector at a Level-1 trigger rate of 100 kHz.

These proceedings collect the presentations given at the first three meetings of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC", held at the Frascati National Laboratories in 2006. The first part of these proceedings contains pedagogical introductions to several basic topics of both theoretical and experimental high pT LHC physics. The second part collects more specialised presentations.

Abstract

To sustain and extend its discovery potential, the Large Hadron Collider (LHC) will undergo a major upgrade in the coming years, referred to as High Luminosity LHC (HLLHC), aimed to increase its instantaneous luminosity, 5 times larger than the designed limit, and, consequently leading to high levels of radiation, with the goal to collect 10 times larger the original designed integrated luminosity. The drift tube chambers (DT) of CMS muon detector system is built to proficiently measure and trigger on muons in the harsh radiation environment expected during the HL-LHC era. Ageing studies are performed at the CERNs gamma ray irradiation facility (GIF++) by measuring the muon hit efficiency of these detectors at various LHC operation conditions. One such irradiation campaign was started in October 2017, when a spare MB2 chamber moved inside the bunker and irradiated at lower acceleration factors. Two out of twelve layers of the DT chamber were operated while being irradiated with the radioactive source and then their muon hit efficiency was calculated in coincidence with other ten layers which were kept on the standby. The chamber absorbed an integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway and strategies to mitigate the aging effects are also being developed. The effect of radiation on the performance of DT chamber and its impact on the overall muon reconstruction efficiency expected during the HL-LHC are presented.